Chicken embryos at 11 days incubation are killed by intravenous inoculation of small numbers of virulent colony types T1 and T2, of Neisseria gonorrhoeae and are relatively resistant to colony types 3 and 4. The embryos may be protected by prior treatment of the inocula with normal and immune sera. This experimental model is being investigated to develop information bearing on attributes of virulence of the gonococcus and antigen antibody systems which may be involved in protection against gonorrhea in man.